(466a) Increase the Feeding Value of Corn Ethanol Coproducts Via Genetic Engineering of Yeast

With fast growth in recent several years, the U.S. corn ethanol industry provides enormous amount of co-products, for instance, distiller dried grains with solubles (DDGS), to the feed market, making the ethanol industry as one of the largest contributors to the US feed supply. Although DDGS is a good source for protein, the low content and low digestibility of several essential amino acids (lysine, methionine, threonine, arginine and tryptophan) is a limiting factor when considering the inclusion of DDGS in animal diets and its impact on animal performance. High inclusion of DDGS in animal diets causes amino acid imbalances with subsequent consequences on animal performance and excess excretion of nitrogen into the environment. Addition of synthetic sources of amino acids can alleviate amino acid imbalances and result in significant decreases in the nitrogen discharge and manure odor. Commercially available synthetic amino acids for feed supplementation are only available for some amino acids while costs can fluctuate if supplies are short. Many amino acids remain too costly for commercial feeding purposes. Regardless of the availability of amino acid supplements, the value of an ingredient such as DDGS is improved if the content and digestibility of limiting amino acids such as lysine, tryptophan and arginine are increased. Saccharomyces cerevisiae has been considered as a natural food product. Non-living dry yeast powder can often be used as a food supplement for human nutritional and pharmaceutical purposes. In corn ethanol co-products, yeast biomass is an important composition and is expected to provide more of these limiting amino acids. Although genetic modification of yeast has been intensively carried out to improve the baker’s yeast for ethanol production and some of the engineered strains have been implemented and commercialized for industrial ethanol production, no genetic engineering research has been specifically focused on the animal feed improvement for the corn ethanol coproducts. Using genetic manipulation to engineer yeast strains is considerably easier than engineering feed grains while engineered yeast is also more likely to be adopted by the industry. The goal of this study is to significantly increase the feeding value of corn ethanol coproducts through genetically engineering the yeast strain to enrich several key amino acids (first limiting lysine, commercial costly tryptophan and arginine) during the fermentation so that the yeast biomass can significantly improve the nutritional value of DDGS. Specifically, the metabolic pathway of lysine, arginine and tryptophan in S. cerevisiae is genetic engineered to generate the biomass with more of these amino acids. Quite different from the current mainstream emphasis on the ethanol production, this research focuses on the improvements of animal feeds generated from corn ethanol industry and will potentially benefit all sides involved in this industry, including the animal feeds and the corn farmers, and potentially decrease the environmental impacts of the whole corn ethanol industry.